Sag, ball and rod mills are used in the minerals industry to grind ore into small particles. Typically, the mills comprise cylindrical-shaped steel milling chambers partially filled with a mill charge or grinding media such as steel balls for sag and ball mills or steel rods for rod mills. A conveyor or hopper moves ore gravel into the mill and the mill is rotated causing the steel balls or rods themselves to cascade, which in turn grinds the ore.
The nature of the intense fracturing and grinding that occurs in the mills requires that the shell of the mill be protected to prevent deterioration. Typically, the protection is achieved by lining the inner wall of the mill shell with plate liners and separate bolted lifters made of hardened steel or combination steel liner/lifter plates may be used.
Depending on the size of the mill, i.e. its diameter and length, there may be well over 100 mill liners and lifters, each typically weighing over 100 kilograms. As the mill is operated, the Intense fracturing and grinding wears the mill liners and lifters, and replacement becomes necessary. The relining process is necessary to maintain the integrity of the mill shell and to improve the efficiency of the mill grinding process by increased material lift from the new lifters and liners.
The relining process involves taking the mill out of service, and sequentially removing the worn liners and lifters and replacing them with new liners and lifters. Typically, liners are retained by lifter bolts through the shell of the mill and these lifter bolts must first be removed before the liners or lifters can be removed from the shell of the mill. To remove a lifter bolt its nut is loosened from the exterior of the mill shell and the lifer bolt is punched through into the mill. Once the lift bolts have been removed, the worn liner and lifter can be removed from the inner wall of the shell and a new liner and lifter can be bolted in place.
It is important that the relining process is undertaken as quickly as possible as any downtime with the mills out of service can be costly and for this reason various handling machines and tools are often used to aid in the relining process. Further, such handling machines and tools are often essential due to the size and weight of the liners and lifters.
One known method of relining a mill involves inserting a into an open end or entry of the mill, for example through the center of the mill's bearing, to form a pathway within the mill along which a handling machine comprising a carriage with a remote handling arm can move. Typically, the carriage's remote handling arm has a grapple assembly or the like for handling mill liners and lifters, and the handling arm is operable to aid in the relining process. Such a device is described in U.S. Pat. No. 3,802,150. Other known handling machines do not use a track within the mill but operate by simply extending a single arm through a large entry point in the mill which can run around the inside of the mill handling and placing liners and lifters.
The handling machines mentioned are suitable for larger mills, for example mills that are 12 meters in diameter, which have large end entry points, for example openings of up to 2 meters in diameter through the mill's end bearing. However, generally these machines can not be used in smaller mills with small entry points or openings. Therefore, the relining process for smaller sized mills conventionally involves removing and replacing liners and lifters by hand. This can be a time consuming and costly operation, not only because of the mill downtime but because a significant amount, of manual labour is required. Further, relining a mill by hand only can be risky to those involved from a safety viewpoint.
It is an object of the present invention to provide an alternative mill relining apparatus.